<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
    <style>
        .box {
            width: 200px;
            height: 200px;
            border: 1px solid red;
        }
        .con {
            width: 100px;
            height: 100px;
            border: 1px solid #000;
            margin: 50px auto;
        }
    </style>
</head>
<body>
    <div class="box">
        <div class="con"></div>
    </div>

    <script>
        var boxELe = document.querySelector('.box')
        var conEle = document.querySelector('.con')

        // boxELe.onmouseover = function(){
        //     console.log('big  mouseover')
        // }
        // boxELe.onmouseout = function(){
        //     console.log('big mouseout')
        // }

        boxELe.onmouseenter = function(){
            console.log('mouse enter')
        }

        boxELe.onmouseleave = function(){
            console.log('mouse leave')
        }

        
    </script>
</body>
</html>